Amped Wireless has announced a "high power" AC USB adapter.
The UA230A High Power Wi-Fi USB Adapter is a 1×1 AC580 class dual-band USB 2.0 adapter. 
Amped claims that a removable external 3 dBi dual-band antenna and internal power amplifiers provide "up to twice the range of standard Wi-Fi adapters and up to three times the speed".
Amped Wireless UA230A
The UA230A comes with Windows and Mac OS drivers and starts shipping at the end of this month. MSRP is $49.99 and it can be pre-ordered now direct from Amped Wireless.